The present invention relates to a system for both detection of the presence of, and for remote identification of or telemetry of data to or from, objects using electronically interrogatable coded labels. In particular the invention relates to a system for automated detection of the presence of labels attached to merchandise, and automated input to or extraction of data from those labels.
An electronic label, the presence of which may be detected by field disturbance principles without the particular label being then identified, but which is also capable of carrying electronically coded data, may be attached to an article of merchandise.
An electronic system called a presence detection interrogator and containing an antenna which creates an electromagnetic field in an exit region from a shop is able to detect the occurrence of an article tagged with one of the labels passing through the field. When the presence of the label is so detected an alarm is raised, as it is presumed that the article has not been paid for. However, if the article has been properly paid for, the label can at the point of sale be removed or have its presence indicating function disabled, so that no alarm is raised when that label passes through a scanned area.
As well as having a capacity to signal its presence through field disturbance, the label may be electronically encoded with data which may be read either by presence detection means or data communications means. The presence detection means may include a presence detection signal generator, a presence detection antenna for creating a presence detection electromagnetic field, and an analyser of impedance associated with the presence detection antenna. The data communications means may include a generator of an interrogation signal, an interrogation antenna for creating an interrogation electromagnetic field, a data receiver antenna, and a receiver and decoder of data communication signals. The signals received and decoded by the receiver and decoder may be presented as an output signal to a data processing system.
Although the present invention is herein described with reference to a merchandising operation, it is to be appreciated that it is not thereby limited to such application. Thus the presence and data label can be applied to object identification operations generally, and has obvious uses in libraries and in document control environments.
A simplified diagram of the system is shown in FIG. 1A wherein a labelled item 1 carries an electronic label 2, the presence of which (assuming that function is not disabled) can be detected by a presence sensing antenna 3 connected to a label presence detector 4 and providing, when a label is detected, a label presence output signal LPO. Data which is present within label 2 may be extracted therefrom by a data interrogation antenna (DIA) 5 which is connected to a data communications interrogator (DCI) 6. Referring to FIG. 1B when it is desired that label 2 should produce no signal from presence detector 4 (ie. item 1 has been paid for), label 2 is placed over a disabling plate 7 which upon receipt of a disabling input signal DIS to a disabling signal generator 8, generates a disabling electromagnetic field. The latter changes the nature of a circuit contained within label 2 in a manner to be described herein.
The disabling system may also contain means to change or to read the data within label 2 and also to provide a programming signal to label 2 so that the data may be changed. In this way reading of the label's data may be performed to signal to or to confirm that the presence signalling section of label 2 has been legitimately disabled.
In the construction of presence detection and data carrying labels, an important design parameter is the physical size of the antenna section of the label, as both presence detection range and data interrogation range depend upon the size of that antenna. It is therefore desirable that the antenna for either of these operations be made as large as possible. One way in which this may be achieved is to make a single antenna connected to appropriate circuit elements fulfill both of the presence detection and data communication functions. Another approach is the employment of separate antennas, together with ensuring that their size and relative positioning is such as to permit a maximum antenna size consistent with any necessary separation of the functions of presence detection and data communication.
In the achievement of sufficient range for both data communication operations and presence detection operations, note should be taken of electromagnetic compatibility regulations which limit the value of electromagnetic field which may be legally established for each of these two functions. In many jurisdictions a CISPR quasi-peak detector is the instrument specified for making measurements of fields which are to be compared against regulations. Because the response of that measuring instrument depends on a complex and in some aspects non-linear way upon both the field amplitude and its time dependence, it is appropriate in the achievement of long range for both of the functions fulfilled by the label, that the electromagnetic signals which perform these functions, and the response of the label to those signals, should be shaped to achieve the largest possible range achievable within the regulations. This requirement needs to be taken into account in both the design of the label and the design of possibly combined or possibly separate interrogator systems for functions of the label.
In the practical operation of systems as described herein it may be necessary to disable the presence detection section of a label to indicate that the attached item has been paid for. One method by means of which such disabling may be carried out is to subject the presence signalling section of the label to an intense electromagnetic field at a frequency of resonance of that section so as to produce failure of one of the presence signalling circuit elements. It is normally desired that the data communication section of the labels survive this operation, and the latter section should therefore be designed accordingly.
In the design of systems which have the capability for both presence detection and data transmission, it is necessary to take into account the frequencies normally used for exploitation of these functions. In respect of presence detection, resonance of the label within the frequency band 8.0-8.4 MHz is frequently employed, but other frequencies seem to be equally useful under the regulations, although spectral occupancy by other users may be a relevant consideration. For data communication, the frequencies 27.12 MHz, 13.56 MHz and 6.78 MHz are useful in that electromagnetic compatibility regulations allow, within a narrow band surrounding these frequencies, transmissions of significantly greater amplitude (by 20 dB and sometimes by a much greater amount) than in the immediately adjacent bands. The greatest range can be achieved if it can be arranged that the label antenna in the data communication mode of the label is resonant at one or other of these frequencies.